anatomy of the orbit - thieme connect...2020/09/17 · and maxillary sinus (posterior wall). the...

Anatomy of the OrbitStefan Lieber1 Juan C. Fernandez-Miranda1

1Department of Neurosurgery, Stanford University Medical Center,Palo Alto, California, United States

J Neurol Surg B 2020;81:319–332.

Address for correspondence Juan C. Fernandez-Miranda, MD,Department of Neurosurgery, Stanford University Medical Center,875 Blake Wilbur Drive, Palo Alto, CA 94304, United States(e-mail: [email protected]).

Osteology of the Orbit

The orbit is a paired, transversely oval, and cone-shapedosseous cavity.Whenmeasured fromthesupraorbital foramento the anterior genu of the cavernous internal carotid artery, itslength in the anterior–posterior axis averages 63mm.1

The orbital walls constitute a significant portion of theanterior and middle cranial base and are formed by sevenbones: frontal, zygomatic, maxillary, lacrimal, ethmoid, pal-atine, and sphenoid (►Figs. 1–4).2

The orbital rim is formed by the frontal, zygomatic, andmaxillary bones. In the superomedial aspect of the frontalbone, the supraorbital nerve and artery exit the orbit via the

supraorbital notch or foramen. The zygomatic process of thefrontal bone joins with the frontal process of the zygomaticbone at the frontozygomatic suture superolaterally. Themaxillary bone forms most of the inferomedial rim ofthe orbit, and its frontal process meets the frontal bone atthe frontomaxillary suture.

The orbital roof is composed of the orbital plate of thefrontal bone anteriorly and the lesser wing of the sphenoidbone posteromedially. Two shallow depressions exist in theanterior orbit just behind the rim: superomedially, thetrochlear fossa accommodates the trochlear apparatus, aligamentous hypomochlion for the superior oblique muscle;superolaterally, the lacrimal gland rests in the lacrimal fossa.

Keywords

► orbit► microsurgical

anatomy► extraocular muscles► annular tendon► annulus of Zinn► skull base► cranial nerves► optic nerve► oculomotor nerve► trochlear nerve► abducens nerve► trigeminal nerve► facial nerve► optic canal► superior orbital

fissure► orbital apex► ciliary ganglion► ophthalmic artery

Abstract The orbit is a paired, transversely oval, and cone-shaped osseous cavity bounded andformed by the anterior and middle cranial base as well as the viscerocranium. Its maincontents are the anterior part of the visual system, globe and optic nerve, and theassociated neural, vascular, muscular, glandular, and ligamentous structures requiredfor oculomotion, lacrimation, accommodation, and sensation.A complex stream of afferent and efferent information passes through the orbit, whichnecessitates a direct communication with the anterior and middle cranial fossae, thepterygopalatine and infratemporal fossae, as well as the aerated adjacent frontal,sphenoidal, and maxillary sinuses and the nasal cavity.This article provides a detailed illustration and description of the microsurgicalanatomy of the orbit, with a focus on the intrinsically complex spatial relationshipsaround the annular tendon and the superior orbital fissure, the transition fromcavernous sinus to the orbital apex. Sparse reference will be made to surgicalapproaches, their indications or limitations, since they are addressed elsewhere inthis special issue. Instead, an attempt has been made to highlight anatomicalstructures and elucidate concepts most relevant to safe and effective transcranial,transfacial, transorbital, or transnasal surgery of orbital, periorbital, and skull basepathologies.

published onlineSeptember 17, 2020

© 2020 Georg Thieme Verlag KGStuttgart · New York

DOI https://doi.org/10.1055/s-0040-1715096.ISSN 2193-6331.

Review Article 319

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Published online: 2020-09-17

mailto:[email protected]

https://doi.org/10.1055/s-0040-1715096

https://doi.org/10.1055/s-0040-1715096

Fig. 1 Osteology of the Orbit I. (A) Oblique view of a right orbit, oriented along the axis of the optic canal. The orbit is formed by seven bones(the lacrimal bone is missing in this specimen). (A′) Enlarged view of (A), detailing the optic canal and the superior orbital fissure. (B) Osteology ofthe anterior and middle cranial fossae. (C) Osteology of the sellar region, oblique view oriented along the axis of a right optic canal. (A–C:macerated skull specimen). 1, frontal bone; 2, zygomatic bone; 3, maxillary bone; 4, middle turbinate (the lacrimal bone is missing in thisspecimen); 5, ethmoid bone; 6, orbital process of the palatine bone; 7, sphenoid bone: 7a lesser wing, 7b greater wing, 7c body; 8, supraorbitalnotch (or foramen); 9, zygomatic process of the frontal bone; 10, frontal process of the zygomatic bone; 11, frontozygomatic suture; 12, frontalprocess of the maxillary bone; 13, infraorbital foramen; 14, anterior lacrimal crest (maxillary bone); 15, site of the posterior lacrimal crest (thelacrimal bone is missing in this specimen); 16, trochlear fossa; 17, frontomaxillary suture; 18, frontonasal suture (nasion); 19, infraorbitalgroove; 20, posterior ethmoidal foramen; 21, anterior ethmoidal foramen; 22, anterior clinoid process; 23, optic canal; 24, superior orbitalfissure; 25, optic strut; 26, crista galli; 27, cribriform plate of the ethmoid bone; 28, planum sphenoidale; 29, orbital plate of the frontal bone; 30,foramen rotundum; 31, foramen ovale; 32, dorsum sellae; 33, lingual process of the sphenoid bone; 34, lateral tubercular crest; 35, limbussphenoidale; 36, tuberculum sellae.

Journal of Neurological Surgery—Part B Vol. 81 No. B4/2020

Anatomy of the Orbit Lieber, Fernandez-Miranda320

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Fig. 2 Osteology of the Orbit II. (A) Antero-oblique view of a right orbit. The zygomatic, maxillary, and lacrimal bones have been removed forbetter visualization. (B) A right orbit as seen from below. (C) The palatine bone as seen from an anteromedial perspective, right side. (D) Theethmoid bone, anterior view. (E) The maxillary bone as seen from above, right side. (A–E: disarticulated macerated skull specimen). 1, superiororbital fissure; 2, optic canal; 3, lacrimal foramen; 4, frontoethmoidal suture; 5, ethmoidal cells; 6, orbital plate of the ethmoid bone (laminapapyracea); 7, perpendicular plate of the palatine bone; 8, foramen rotundum; 9, orbital process of the palatine bone; 10, frontosphenoidalsuture; 11, orbital plate of the frontal bone; 12, trochlear fossa; 13, foramen cecum; 14, perpendicular plate of the ethmoid bone; 15, cribriformplate of the ethmoid bone; 16, supraorbital notch (or foramen); 17, sphenoidal process of the palatine bone; 18, sphenopalatine notch orforamen (leads to pterygopalatine fossa); 19, horizontal plate of the palatine bone; 20, crista galli; 21, superior meatus; 22, middle nasal concha;23, infraorbital foramen; 24, infraorbital groove; 25, orbital plate of the maxillary bone; 26, frontal process of the maxillary bone; 27, anteriorlacrimal crest.


Anatomy of the Orbit Lieber, Fernandez-Miranda 321

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Fig. 3 Endoscopic endonasal perspective of the orbit. (A): Optic nerve, anterior ICA genu, and the lateral opticocarotid recess are importantlandmarks for reliable identification of the orbital apex, left side. (B): A, following complete bone removal. (C): Inferomedial aspect of the orbit,and spatial relationships with the maxillary sinus, the palatine bone, and the pterygopalatine fossa. (D): Enlarged view of (C). (E): Ethmoidal cells,olfactory fibers, and the cribriform plate, view toward the frontal base, centered to the left. (F): E after complete removal of the ethmoidal cellsand the lamina papyracea to expose the ethmoidal arteries and the periorbita. (G): A left periorbita, 45 degrees optic. (H): G, following removalof periorbita and intraconal fat to expose the optic nerve, globe, and extraocular muscles. (A–H: formalin-fixed, silicone injected cadavericspecimen). ICA, internal carotid artery; IR, inferior rectus muscle; MR, medial rectus muscle; SO, superior oblique muscle; 1, optic canal; 2,planum sphenoidale; 3, internal carotid artery (anterior genu); 4, lateral opticocarotid recess (which represents a pneumatized optic strut); 5,sphenoid sinus (anterior wall); 6, optic nerve; 7, ophthalmic artery; 8, maxillary strut; 9, superior orbital fissure; 10, periorbita (continuation ofperiosteal dura mater); 11, maxillary sinus; 12, orbital plate of the ethmoid bone (lamina papyracea); 13, sphenopalatine notch or foramen(leads to pterygopalatine fossa); 14, perpendicular plate of the palatine bone (medial wall of the maxillary sinus); 15, sphenoidal process of thepalatine bone; 16, infraorbital nerve; 17, olfactory fibers (through the cribriform plate); 18, ethmoidal cells; 19, frontal sinus; 20, perpendicularplate of the ethmoid bone; 21, posterior ethmoidal artery and nerve; 22, anterior ethmoidal artery and nerve; 23, globe; 24, annular tendon (or“annulus of Zinn”); 25, smooth orbital muscle (covering the inferior orbital fissure).



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Fig. 4 Anterior orbital and periorbital space, orbital septum, lacrimal gland. (A) Osteology of the lateral orbit. (B–D) Stepwise illustration offacial nerve branches, orbicularis oculi muscle, orbital septum, the superior tarsal plate, and lacrimal gland. (E, F) Detail of the lateral orbitaltubercle which serves as the attachment for the superior and inferior crura of the lateral canthal tendon. (G) Supraorbital artery andsupratrochlear vein, exiting the orbit via the supraorbital notch and the trochlear fossa, respectively. (A, E: macerated skull specimen, B–D and F,G: formalin-fixed, silicone injected cadaveric specimen). 1, frontozygomatic suture; 2, temporozygomatic suture; 3, zygomaticofacial foramenor foramina; 4, jugal point (frontal process meets temporal process of the zygomatic bone); 5, superficial temporal artery (frontal branch); 6,temporalis muscle; 7, orbicularis oculi muscle (orbital part); 8, facial nerve (branches to the orbicularis oculi and frontalis muscles); 9, orbitalseptum; 10, inferior lateral palpebral artery; 11, superior lateral palpebral artery; 12, lacrimal gland (orbital part); LP, levator palpebrae muscle;13, lateral orbital tubercle (or “tubercle of Whitnall”); 14, inferior orbital fissure; 15, superior tarsal plate (serves as the attachment for theaponeurosis for the levator palpebrae muscle); 16, superior and inferior crura of the lateral canthal tendon, lateral canthal ligament (lateralcanthus); 17, supraorbital artery; 18, medial canthus; 19, supratrochlear vein.



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The lateral wall is composed of the frontal process of thezygomatic bone anteriorly and the greater wing of thesphenoid posteriorly. The superior orbital fissure separatesthe lesser (superomedial) from the greater (inferolateral)wing of the sphenoid. Except for the lacrimal foramen (whichtransmits the recurrent meningeal artery, a branch of theophthalmic artery) and the miniscule zygomatico-orbitalforamina (which transmit the zygomaticofacial and zygo-maticotemporal branches of the maxillary nerve), there areno osseous channels in the lateral wall.

The orbital floor is mostly formed by the orbital surface ofthe zygomatic bone anterolaterally and the orbital plate ofthe maxillary bone medially. The contribution of the orbitalprocess of the palatine bone to the orbital floor ismarginal; itis an important structure, however, which also partakes inthe formation of the pterygopalatine fossa (anterior wall)and maxillary sinus (posterior wall). The inferior orbitalfissure separates the orbital floor from the lateral wall, andthe infraorbital groove emerges from it in a more medialtrajectory toward the infraorbital canal, which transmits theinfraorbital nerve and vessels.

The medial wall is far more complex: the lacrimal groove,which accommodates the lacrimal sac, is bounded by theanterior lacrimal crest of themaxillary bone and the posteriorlacrimal crest of the lacrimal bone, and it opens into the nasalcavity inferomedially to transmit the nasolacrimal duct. Moreposteriorly, the lacrimalboneconnectswith theorbital plateofthe ethmoid bone, better known as the lamina papyracea, andeventually the sphenoid bone. At the level of the frontoeth-moidal suture, the anterior and posterior ethmoidal foramina(generally between one and four in number, but most com-monly two) connect the orbit with the nasal cavity.3 Theytransmit their respective ethmoidal arteries (branches of theophthalmic artery) and ethmoidal nerves (branches of thenasociliary nerve). When measured in the anterior–posterioraxis, the anterior ethmoidal foramen is located 21mm poste-rior to the anterior lacrimal crest of the maxillary bone, theposterior ethmoidal foramen14mmfurther posterior, and theoptic canal another 6mm posterior.3

The optic canal is formed by the body and lesser wing of thesphenoid bone. It is transverselyoval-shaped, projects oblique-ly anterolaterally when viewed from its intracranial os, andopens into thesuperomedial aspectof theorbital apex. The roofof the optic canal is formed by an osseous bridge that extendsfrom the limbus sphenoidale (body of the sphenoid) mediallyto the lesserwing laterally; theanteriorclinoidprocessprojectsposterolaterally and forms the lateral wall of the optic canal,while the medial wall faces the sphenoid sinus.

The floor of the optic canal is formed by the optic strut,which continues to form the base of the anterior clinoidprocess and separates the optic canal from the superior orbitalfissure. Fromthe endonasal perspective,pneumatizationof thebase of the optic strut represents the lateral opticocarotidrecess. The superior orbital fissure provides the communica-tion between the middle cranial fossa and the orbit and ismostly bounded by the lesser wing of the sphenoid super-omedially, the greater wing laterally, and the body of thesphenoid bone medially. The mid-portion of the lateral edge

serves as a site of attachment for the annular tendon. Theinferior aspect of the superior orbital fissure is separated fromthe foramen rotundum by the maxillary strut.

The inferior orbital fissure represents the incompleteborder between the orbit’s lateralwall, formed by the greaterwing of the sphenoid bone, and the orbital floor, formedmostly by the orbital plate of the maxillary bone and, to a farlesser extent, the orbital process of the palatine bone. Theinferior orbital fissure communicates with the pterygopala-tine fossa posteromedially, and the infratemporal and tem-poral fossae anterolaterally.

Anterior Orbital and Periorbital Space,Orbital Septum, and the Lacrimal Gland

Underneath the skin, the orbicularis oculi muscle covers thecircumference of the orbit; it consists of the orbital, presep-tal, and pretarsal parts (►Fig. 4).2,4 The orbital part arisesfrom the osseous orbital rim, namely, the frontal, zygomatic,andmaxillary bones and coversmost of the orbit; it serves asthe sphinctermuscle of the eyelids and blends into themimicmusculature and the facial fascia peripherally. The eyelidsaccommodate the pretarsal partwhich is the continuation ofthe medial and lateral palpebral ligaments; its prime func-tion is eye closure. The preseptal part lies between the orbitaland pretarsal parts. The orbital septum underlies the orbi-cularis oculimuscle and represents the anterior border of theorbit. The superior and inferior tarsal plates shape the eyelids, and their medial and lateral extensions blend into thepalpebral ligaments, the suspension of the eye lids. In theupper lid, the levator palpebrae muscle broadens into anaponeurosis which inserts broadly on the anterior surface ofthe superior tarsal plate. Themedial canthal ligament dividesto insert at the superior aspect of the anterior and posteriorlacrimal crests, whereas the lateral canthal ligament insertsat the lateral orbital tubercle (or “tubercle of Whitnall”), anosseous prominence slightly posterior to the orbital rim and10 to 12mm posteroinferior to the frontozygomatic suture.

The lacrimal gland is an exocrine gland located in thelacrimal fossa, a depression in superolateral aspect of theorbit, considered a minor salivary gland. The gland consistsof two lobes; the bigger orbital lobe lies superior and thesmaller palpebral lobe deep to the aponeurosis of the levatorpalpebrae muscle.

The temporal and zygomatic branches of the facial nerveascend over the mid-portion of the zygomatic arch to reachthe frontalis and orbicularis oculi muscles. Sensation of thecornea, eyelids, and the periorbital region is transmitted bythe nasociliary, supratrochlear, supraorbital, and lacrimalbranches of the ophthalmic division of the trigeminal nerve,and the infraorbital, zygomaticofacial, and zygomaticotem-poral branches of the maxillary nerve.1,5

Orbital Apex, Annular Tendon, and theExtraocular Muscles

The orbital apex is an immensely complex anatomical re-gion: first, it represents the intersection of neurovascular



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structures entering from and exiting into the lateral com-partment of the cavernous sinus and the optic canal with theorbital space (►Figs. 3, 5–7).1,2,5,6 Second, it is the sitewherethe dura mater of the middle cranial fossa and the cavernoussinus blends into the dura mater of the superior orbitalfissure, the optic nerve sheath, and the periorbita and formsan annular tendon fromwhich the four rectus muscles arise.The annular tendon, also known as the “annulus of Zinn,”encloses the optic nerve, the ophthalmic artery, and mostcranial nerves associated with vision, oculomotion, andaccommodation. The notable exceptions to this are thetrochlear nerve, and the lacrimal and frontal nerves(branches of the ophthalmic division of the trigeminalnerve). The annular tendon is attached around the superior,inferior, and medial aspects of the optic canal and the mostmedial aspect of the lateral margin of the superior orbitalfissure, formed by the sphenoid’s greater wing. Since it onlyencircles the optic canal and the mid-portion of the superiororbital fissure, it in turn subdivides the superior orbitalfissure into three separate compartments: a superolateral,a central, and an inferomedial compartment (►Fig. 6).

The superolateral compartment is traversed by the lacri-mal and frontal nerves of the trigeminal nerve’s ophthalmicbranch, the trochlear nerve and the superior ophthalmicvein. The central compartment (or oculomotor foramen)contains all neurovascular structures that enter and exitthe orbit through the annular tendon and course withinthe intraconal space. These are the superior and inferiordivisions of the oculomotor nerve, the nasociliary nerve, theabducens nerve, and the parasympathetic and sensory fibersof the ciliary ganglion via the superior orbital fissure, as wellas the optic nerve and the ophthalmic artery via the opticcanal. The inferomedial compartmentonly accommodates theinferior ophthalmic vein and avarying number of branches ofthe carotid sympathetic plexus, the sympathetic contribu-tion to the ciliary ganglion. The inferior boundary of theinferior compartment is formed by the remnant of theinferior smooth orbital muscle, which covers the entirelength of the inferior orbital fissure, and thereby separatesthe orbit from the temporal, infratemporal, and pterygopa-latine fossae.7 This muscle blends into the periosteum of theorbital floor. The infraorbital nerve, artery, and vein courseunderneath the orbital periosteum.

The superior, lateral, medial, and inferior rectus musclesarise from the annular tendon to form a muscular cone(►Figs. 5, 7 and 9). The annular tendon represents theproximal end, whereas the globe represents the anterior ordistal end. This cone is sheathed by the periorbita, a thinmembrane, and densely filled with fat invested with adelicate system of ligaments (Koornneef’s bands) whichsurrounds the intraconal neurovascular contents.

The superior rectus muscle courses anteriorly to attach tothe sclera of the globe, �7.5mm posterior to the margin ofthe cornea. It courses directly underneath the levator palpe-brae muscle; both muscles share a soft fascia.

The lateral rectus muscle originates from the annulartendon over the greater sphenoid wing, whereas the medialrectus muscle originates from the annular tendon lateral of

the optic canal; they attach to the medial and lateral sclera,�7 and 5.5 mm posterior to the corneal limbus, respectively.

The inferior rectus muscle courses anteriorly and piercesthe retractor band of the lower lid (the capsulopalpebralfascia).

The superior oblique muscle does not originate from theannular tendon but from the periorbita superomedial to theoptic canal. It courses anteriorly within the superomedialaspect of the intraconal space to reach the trochlear fossa.Here, its tendon is redirected by a ligamentous trochlea(trochlear hypomochlion), and it travels in a posteromedialdirection underneath the superior rectus muscle to eventu-ally insert on the sclera deep to the superior rectus belly.

The inferior oblique muscle is unique in that it does notoriginate from the annular tendon or orbital apex but fromthe inner aspect of the inferior orbital rim between thelacrimal fossa and the zygomaticomaxillary fissure. Itcourses laterally, inferior to the inferior rectus muscle toattach to the sclera deep to the lateral rectus muscle, at thearea corresponding to the macula.2,4,5

Cranial Nerves Associatedwith the Orbit andthe Ciliary Ganglion

Special Sensory InnervationThe optic nerve can be subdivided into five segments:intraocular, intraorbital, intracanalicular, preforaminal, andcisternal; the two last segments represent the intracranialsegments. The optic nerve emerges from the optic chiasmand courses anteroinferolaterally, usually at a 30- to 45-degree angle, within the chiasmatic cistern. In this segment,the optic nerve is transversely oval shaped, and its diametersaverage 5 by 3mm.1 The preforaminal segment refers to theshort segment where the nerve runs underneath the falci-form ligament, a dural fold extending from the limbussphenoidale to the anterior clinoid process but has yet toenter the osseous optic canal (►Fig. 5). It is a short segment,measuring a mere 3 to 5mm, and is surrounded by cerebro-spinal fluid.1 The optic nerve’s intracanalicular segmentpasses through the proper osseous optic canal, whereasthe intraorbital segment is densely surrounded by fat andthe complex neurovasculature of the intraconal space. Theintraocular segment represents the optic nerve within thesclera of the globe, also known as the optic disc.

Once the optic nerve emerges from its osseous canal, itretains its dura and arachnoid protective cover; therefore, acontinuous subarachnoid space exists, extending from themost proximal cisternal segment to the sclera of the globe. Asdiscussed earlier, the optic nerve’s dural sheath blends intothe periorbita and participates on the formation of thesuperomedial aspect of the annular tendon.2

Motor InnervationThe oculomotor nerve courses within its interdural cistern toenter the roof of the cavernous sinus just below the anteriorclinoid process; it splits into superior and inferior divisionsright before entering the orbit. Both divisions take a medialcourse just lateral to the optic strut to pass through



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the central compartment of the superior orbital fissure(►Figs. 5–9).

The smaller superior division consists of the motorbranches to the superior rectus and levator palpebrae

muscles; these branches ascend lateral to the optic nerveand insert to the inner surface of their respective muscles,the latter after passing through the substance of the superiorrectus.

Fig. 5 Optic canal, falciform ligament, and the orbital apex. (A-A”) Detail of the cisternal, preforaminal, intracanalicular, and intraorbitalsegments of the optic nerve from the transcranial and (B) endonasal perspective. (C-F) Stepwise illustration of the cavernous sinus, the superiororbital fissure, and the orbital apex. Lateral view, right side. (A-F: formalin-fixed, silicone injected cadaveric specimen). CN I, olfactory nerve; CNII, optic nerve; IR, inferior rectus muscle; LR, lateral rectus muscle; SR, superior rectus muscle; 1, planum sphenoidale; 2, falx cerebri; 3, limbussphenoidale; 4, anterior clinoid process; 5, falciform ligament; 6, lateral opticocarotid recess (the equivalent of the optic strut from theendonasal perspective); 7, foramen rotundum; 8, foramen ovale; 9, sphenoid sinus; 10, pterygopalatine fossa and branches of the internalmaxillary artery; 11, pterygoid venous plexus.



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The inferior division has a greater diameter and gives riseto motor branches to the medial rectus, inferior rectus andinferior oblique muscles, as well as to pupillary fibers (seeparagraph on “ciliary ganglion”).

The trochlear nerve is the only cranial nerve associatedwith oculomotionwhich does not enter the orbit through theannular tendon. It courses adjacent to and superomedial tothe frontal nerve to eventually blend into the superior aspectof the superior oblique muscle.

Sensory InnervationThe first two branches of the trigeminal nerve are associatedwith the orbit. The ophthalmic nerve, the smallest branch ofthe trigeminal nerve, is embedded in the dura mater of thecavernous sinus’ lateral wall and separates into the lacrimal,frontal, and nasociliary nerves before entering the superiororbital fissure.

The lacrimal nerve enters the orbit via the superolateralcompartment of the superior orbital fissure and coursesalong the superiormargin of the lateral rectusmuscle towardthe lacrimal gland. During its course, it receives postgangli-onic parasympathetic fibers ascending from the pterygopa-latine ganglion via the zygomatic nerve.

The frontal nerve, a branch of the ophthalmic division ofthe trigeminal nerve, rests on the levator palpebrae muscle,immediately underneath the periorbita, having entered theorbit via the superolateral compartment; it divides into a

supraorbital nerve and a supratrochlear nerve. The supraor-bital nerve travels anteriorly along the medial aspect of thelevator palpebrae and superior rectus muscles, accompaniedby its respective arterial branch, to exit the orbit through anotch or foramen in the supraorbital rim. The smaller supra-trochlear nerve courses more medially toward the trochlearfossa, again accompanied by its respective arterial branch, topierce through the orbital septum to exit the orbit near thetrochlea.

The nasociliary nerve is the only trigeminal branch to passthrough the annular tendon and the central compartment ofthe superior orbital fissure. It gives rise to the sensory root ofthe ciliary ganglion (preganglionic parasympathetic fibers,see paragraph on “ciliary ganglion”) and the long ciliarynerves, which transmit sympathetic fibers to the globe(►Figs. 6, 7 and 9). Both short and long ciliary nerves enterthe sclera in proximity to the optic nerve, joined by theposterior ciliary arteries. The nasociliary nerve ascends overthe optic nerve, coursingmedially to give raise to the anteriorand posterior ethmoidal nerves, which accompany theirrespective ethmoidal arteries to exit the orbit via the eth-moidal foramina, as well as to the infratrochlear nerve.

The ciliary ganglion is situated on the inferolateral aspectof the optic nerve, between the nerve and lateral rectusmuscles, just anterior to the steep ascending turn of theophthalmic artery(►Figs. 5, 7, and 9). As described in theprevious sections, it receives a motor root, representingparasympathetic fibers running within the oculomotornerve’s inferior division to the inferior oblique muscle, anda sensory root, formed by sensory fibers from the nasociliarynerve (corneal sensation) and postganglionic sympatheticfibers (nerves to the pupillary dilator muscle). The latterascend from the superior cervical ganglion, coursewithin thecarotid sympathetic plexus and reach the orbit via theophthalmic artery and the ophthalmic and abducens nerves.Only the parasympathetic fibers synapse in the ciliary gan-glion to be emitted as the short ciliary nerves responsible forpupillary constriction and accommodation, sympatheticfibers course within the long ciliary nerves. Both short andlong ciliary nerves enter the sclera in proximity to the opticnerve, joined by the posterior ciliary arteries.

Themaxillary nerve passes through foramen rotundum toenter the pterygopalatine fossa. It gives rise to preganglionicfibers to the sphenopalatine ganglion and the infraorbitaland zygomatic nerves, both of which initially course anteri-orly in the orbital floor, deep to the periorbita. The infraor-bital nerve continues in the infraorbital groove and canal toexit via the infraorbital foramen of the maxillary bone,whereas the zygomatic nerve takes a more lateral coursetoward the orbital wall. Its terminal branches, the zygoma-ticofacial and zygomaticotemporal nerves exit via the zygo-maticofacial foramina of the zygomatic bone (►Fig. 4).

The abducens nerve is unique in that it travels freelywithin the cavernous sinus and is not embedded in thedura mater of its lateral wall. It lies just medial to theophthalmic nerve and enters the orbit through the annulartendon. It then turns laterally to insert to the inner surface ofthe lateral rectus muscle.2,5

Fig. 6 The compartments of the superior orbital fissure. This schematicdrawing is based on►Fig. 1A. The annular tendon (white ring) is attachedaround the superior, inferior, and medial aspects of the optic canal and themostmedial aspect of the lateralmargin of the superior orbitalfissure. Sinceit only encircles the optic canal and the mid-portion of the superior orbitalfissure, it in turn subdivides the superior orbital fissure into three separatecompartments: a superolateral, a central, and an inferomedial.



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Arterial Vasculature Associated with theOrbit

The anterior genu of the internal carotid artery (ICA)consists of the cavernous ICA segment before the proximaldural ring, and the short, extracavernous clinoidal ICA

segment between the proximal and distal dural rings.2,6

The clinoidal ICA is fixed to the anteromedial base of theoptic strut by the proximal and distal dural rings, and thesupraclinoidal ICA segment commences once the artery haspassed through the distal dural ring to enter the intraduralspace (►Figs. 3 and 5).

Fig. 7 Orbital apex and intraconal structures. This figure illustrates the complex microanatomy of neurovascular, ligamentous, dural, andmuscular structures around the orbital apex. Bone, periorbita, and intraconal fat have largely been removed for visualization. The right side of aformalin-fixed, silicone injected cadaveric specimen is shown. (A) Superolateral view. (B) Superior view. (C) Superolateral view, the lateral rectus,superior rectus, and levator palpebrae muscles have been removed. (D) Similar to (C), but the nerves have been fanned out for visualization.(E) Lateral view, detail of the ciliary ganglion. (F) Lateral view, detail of the posterior ciliary arteries. (G) Lateral view, detail of the inferior divisionof the oculomotor nerve. centr ret a, central retinal artery; ganglion, ciliary ganglion; IO, inferior obliquemuscle; IR, inferior rectus muscle; lacr a,lacrimal artery; long and short ciliary, long and short ciliary nerves (sympathetic and parasympathetic postganglionic fibers); LP, levatorpalpebraemuscle; LR, lateral rectus muscle; motor root, motor root branching off the inferior division of the oculomotor nerve;MR,medial rectusmuscle; opht a, ophthalmic artery; post ciliary a, posterior ciliary arteries; post ethm a, posterior ethmoidal artery; sensory root, sensory rootbranching off the nasociliary nerve; SO, superior oblique muscle.



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Fig. 8 Extraocular muscles. This figure illustrates the extraocular muscles and their respective sites of origin and attachment at the globe.Periorbita, intraconal fat, orbital septum, and preseptal structures have largely been removed for visualization. The osseous exposurecorresponds to a one-piece frontotemporal-orbitozygomatic craniotomy which is initiated with a MacCarty burr hole. The right side of aformalinfixed, silicone injected cadaveric specimen is shown. (A), globe, as seen from anterior. (B) Anterior view, (C) lateral view, (D) obliqueanterior view, (E) oblique superior view, (F) detail of the origin of the inferior oblique muscle at the anterior lacrimal crest. IO, inferior obliquemuscle; IR, inferior rectus muscle; LP, levator palpebrae muscle; LR, lateral rectus muscle; MR, medial rectus muscle; SO, superior obliquemuscle; SR, superior rectus muscle; 1, FTOZ craniotomy: cut through the orbital ridge lateral to the supraorbital foramen; 2, trochlea within thetrochlear fossa (ligamentous hypomochlion for the superior oblique muscle); 3, supraorbital foramen and supraorbital nerve; 4, inferior orbitalfissure; 5, frontal nerve (ophthalmic branch of the trigeminal nerve); 6, infraorbital nerve (maxillary branch of the trigeminal nerve); 7, FTOZcraniotomy MacCarty burr hole; 8, FTOZ craniotomy cut across the body of the zygoma, starting at the lateral orbital edge to the anterolateraledge of the inferior orbital fissure; 9, lacrimal groove (accommodates the lacrimal sac and the nasolacrimal duct); 10, infraorbital foramen; 11,anterior lacrimal crest.



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Fig. 9 Intraconal structures and extraocular muscles. In this figure, periorbita, intraconal fat, and periorbital structures have largely beenremoved for visualization. The right side of a formalin-fixed, silicone injected cadaveric specimen is shown from its lateral and superolateralaspects. (A) Levator palpebrae muscle and its aponeurosis, the superior tarsal plate. (B) Levator palpebrae muscle reflected to expose thesuperior rectus muscle. (C) Detail of the trochlea, the hypomochlion of the superior oblique muscle. (D) Superior rectus muscle reflected.(E) Lateral rectus muscle reflected to expose the ciliary ganglion. (F, G) Detail of the ciliary ganglion, its afferent and efferent branches, and theretrobulbar microvasculature. (H) Course of the ophthalmic artery and its distal branches. ant ethma, anterior ethmoidal artery; ganglion, ciliaryganglion; IO, inferior oblique muscle; IR, inferior rectus muscle; lacr a, lacrimal artery; long and short ciliary, long and short ciliary nerves(sympathetic and parasympathetic postganglionic fibers); LP, levator palpebrae muscle; LR, lateral rectus muscle; motor root, motor rootbranching off the inferior division of the oculomotor nerve; MR, medial rectus muscle; post ciliary a, posterior ciliary arteries; post ethm a,posterior ethmoidal artery; SO, superior oblique muscle; SR, superior rectus muscle; sup tarsal plate, superior tarsal plate; sensory root, sensoryroot branching off the nasociliary nerve; supratroch a, supratrochlear artery; trochlea, trochlea within the trochlear fossa.



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The ophthalmic artery arises variably from the supra-clinoidal ICA: 54% of the time from the anteromedial aspect,38% from the superomedial aspect, and 7% from the medialaspect (rarely from the clinoidal or cavernous ICA segment).1

Rare, yet important, variations such as a fetal ophthalmicartery entering the orbit via the superior orbital fissure havebeen described (►Figs. 3, 5, and 7).

Between its origin and its entrance into the optic canal,the length of the ophthalmic artery averages 3 to 7mm.1 Itenters the optic canal and courses within the optic nerve’sdural sheath, inferomedial to the optic nerve in 41% of cases,directly inferior in 33%, and inferolateral in 26% of cases.8 Arecurrent branch might emerge from the ophthalmic arteryto supply the intracanalicular, preforaminal, and cisternalsegments of the optic nerve. Most often, the intracranialoptic nerves are supplied by branches of the superior hypo-physeal arteries.

The ophthalmic artery gives rise to the central retinal, longand short ciliary, supraorbital, medial and lateral palpebral,lacrimal, recurrent meningeal, ethmoidal, supratrochlear,and dorsal nasal arteries. The ophthalmic artery exits theoptic canal and the annular tendon at their most lateralaspect, inferior to the intraorbital optic nerve.1 Among itsproximal branches are the central retinal (see paragraphlater) and lacrimal arteries, as well as some long ciliaryarteries and variable muscular branches. The lacrimal arterycourses anteriorly along the superior edge of the lateralrectus muscle. It gives rise to muscular branches, supply tothe lacrimal gland and conjunctiva, and eventually to thelateral palpebral arteries. The ophthalmic artery steeplyloops upward in the immediate proximity of the ciliaryganglion to pass over the optic nerve (in 85% of cases, andin 15%, it crosses below the optic nerve) and to follow amoremedial trajectory.2 It gives rise to the long and short ciliaryarteries, some innominate muscular branches, and mostnotably the supraorbital artery, which courses anteriorly toexit the orbit via the supraorbital notch or foramen.

The ophthalmic artery continues anteromedially andgives off the posterior and anterior ethmoidal arteries whichcourse inferior to the superior oblique muscle to exit theorbit via their respective ethmoidal foramina. From theendonasal perspective, the posterior ethmoidal arterycourses in a medioposterior direction, whereas the anteriorethmoidal artery, which typically has a greater caliber,courses in a more medioanterior direction (►Figs. 3 and 9).

The distal ophthalmic artery then becomes the supra-trochlear artery which parallels the course of the superioroblique and medial rectus muscles. The supratrochlear ar-tery eventually exits the orbit below the trochlea, giving riseto the medial palpebral arteries, the dorsal nasal artery, andother smaller branches.2,6

The central retinal artery is the first branch of the oph-thalmic artery and arises in proximity to the ciliary ganglionbefore the ophthalmic artery ascends steeply to cross overthe optic nerve (►Figs. 5, 7 and 9). It pierces through theoptic nerve’s dural sheath to course anterior adjacent to andmore distally within the optic nerve. The ophthalmic arterythen gives rise to the short and long posterior ciliary arteries;

these arteries enter the sclera in proximity to the optic nervetogether with the long and short ciliary nerves. The anteriorciliary arteries (not shown) emerge from small arterialmuscular branches and enter the sclera in the insertionzone of their respective extraocular muscles.

The ophthalmic artery also supplies the dura mater vialateral and medial systems and may thus partake in thesupply of dural-based lesions. The lateral system includesbranches of the lacrimal artery and the recurrent meningealartery, an inconsistent branch thatmight arise from it to passbackward through the superior orbital fissure. The medialsystem consists of the anterior and posterior ethmoidalarteries that reach the anterior fossa through the ethmoidalcanals.

Venous Vasculature Associated with theOrbit

The superior ophthalmic vein originates in the superomedialaspect of the anterior orbit then traverses the intraconalspace between the optic nerve and the superior rectusmuscle. It then continues its posterior cavernous-sinus-bound course between the superior and the lateral rectusmuscles to exit the orbit via the superolateral compartmentof the superior orbital fissure.

The far more variable inferior ophthalmic vein drains theanteroinferior and lateral aspects of the orbit. It courses inthe inferomedial quadrant, usually between the inferior andlateral rectus muscles, to exit the orbit underneath theannular tendon via the inferomedial compartment of thesuperior orbital fissure. It may eventually merge with thesuperior ophthalmic vein as it passes through the superiororbital fissure to drain into the cavernous sinus, and/or itmay communicate with the pterygoid plexus via the inferiororbital fissure (►Figs. 5 and 6).

Both veins lie mainly within the muscular cone but exitthe orbit outside the annular tendon. They also receive bloodfrom the periorbital region, for example, the angular, supra-orbital, supratrochlear, and facial veins.

The infraorbital vein, which chaperones the infraorbitalnerve and artery on their course through the inferior orbitalfissure, infraorbital canal, and infraorbital foramen, drainsinto the pterygoid plexus. The infraorbital vein, nerve, andartery all course in the orbital floor below the periorbita, andhence are not intraorbital structures in a strict sense.2,6

Conflict of InterestNone declared.

References1 Lang J. Skull Base and Related Structures, 2nd ed. New York:

Schattauer; 20012 Rhoton A. Cranial Anatomy and Surgical Approaches. Philadel-

phia, PA: Lippincott; 20033 Felding UA, Karnov K, Clemmensen A, et al. An applied anatomical

study of the ethmoidal arteries: computed tomographic anddirect measurements in human cadavers. J Craniofac Surg2018;29(01):212–216



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4 Leblanc A. The Cranial Nerves, 2nd ed. Berlin: Springer;1995

5 Lasjaunias P, Berenstein A, terBrugge KG. Surgical Neuroangiog-raphy, 2nd ed. Vol. 1. New York: Springer; 2001

6 Dutton J. Atlas of Oculoplastic and Orbital Surgery, 2nd ed.Philadelphia, PA: Lippincott; 2019

7 De Battista JC, Zimmer LA, Theodosopoulos PV, Froelich SC, KellerJT. Anatomy of the inferior orbital fissure: implications for endo-scopic cranial base surgery. J Neurol Surg B Skull Base 2012;73(02):132–138

8 Renn WH, Rhoton AL Jr. Microsurgical anatomy of the sellarregion. J Neurosurg 1975;43(03):288–298

Review Article332


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anatomy of the orbit - thieme connect...2020/09/17 · and maxillary sinus (posterior wall). the...

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